Core: Add functions to check whether an Entrance/Region/Location exists

[NewSoupVi]

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People are doing goofy shit like

if entrance_name in self.multiworld.regions.entrance_cache[self.player]

and

try:
    self.get_entrance(entrance_name)
except KeyError:
    ...

in their world code. Let's stop that.

Alternatives

We could just make the get_[spot] methods return None if the spot doesn't exist. Maybe we could even add an optional argument called return_none_if_not_exists=False for the sake of worlds already relying on the KeyError behavior. (This would make that function significantly slower though)

We could also make alternative methods called try_get_[spot].

I thought this would be the simplest but I'm obviously willing to hear other opinions

Also:

Are the multiworld versions necessary? I'm not sure whether we should be adding multiworld methods for things at this point, I did it more out of "tradition" than anything

[EmilyV99]

I definitely prefer the try_get_[spot] -> Optional to [spot]_exists -> bool. I have no opinion on if making it a behavior of get_[spot] is better or not, though.

[NewSoupVi]

I definitely prefer the try_get_[spot] -> Optional to [spot]_exists -> bool. I have no opinion on if making it a behavior of get_[spot] is better or not, though.

Imma be honest I kinda just hate the name lol (also getting something to check whether it exists is pretty slow but that'd probably not be so bad, I don't think this would be a hot code path)

[NewSoupVi]

Apparently this is not wanted so I guess someone can close it if they want to, I will never 😭